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Number class
============
Requirements
------------
- Should increase the numerical precision.
- Should fallback to (long) double and use its operators directly,
so that the code could be optimized by the compiler.
- High precision support should be either:
- a run-time option by using plugins (preferred)
- a compile-time option
Options
-------
- static polymorphism: CRTP
- dynamic polymorphism: interface is a usual class with pure virtual methods;
Q_DECLARE_INTERFACE, Q_INTERFACES can be used here
- QVariant/QMetaType allows to create objects dynamically on run-time:
- double can be used directly
- custom types actually too, but dynamic polymorphism needs pointers
- QMetaType::construct() returns void*
- using QVariant in the calculation methods to carry the number and create
a double or the custom type at run-time is possible
Advantages/Drawbacks/Conclusion
-------------------------------
- CRTP allows to inline the methods and using (long) double's operators becomes
possible
- using virtuals does not allow to inline the methods, if pointer or references
to the object are used, which is necessary in the case of dynamic binding
- inlining operators does not work with dynamic polymorphism
- having high-precision and the (long) double fallback needs a common base
Impossible solution(s)
----------------------
1.
- derive the type using (long) double type from a base using CRTP approach
- derive the interface for the dynamic binding also from this base
- derive concrete implementations from the interface
Reason:
- inserting a dynamically created type as template parameter into the CRTP base
is not possible
2.
- use QVariant as data carrier/common base
- mirror QVariant's behaviour in KSpread::Value
Reason:
- the QVariant::Type does not suffice, you need to know the type in order to use
it
Possible solution(s)
--------------------
0.
- the information, which type is in use, that's a QVariant::Type, should be
stored per document, more precisely in CalculationSettings
union
{
double a;
void* b;
};
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